Birthday Paradox Calculator
Calculate the probability that two people share the same birthday in a group
About this calculator
The Birthday Paradox Calculator determines the probability that at least two people in a group share the same birthday. This fascinating mathematical concept reveals counterintuitive results - for example, in a group of just 23 people, there's over a 50% chance that two people share a birthday. The calculator is valuable for understanding probability theory, planning events, and exploring statistical phenomena that challenge our intuitive expectations about random occurrences.
How to use
Enter the number of people in your group into the calculator. Click the calculate button to instantly see the probability percentage that at least two people share the same birthday. The calculator assumes a 365-day year and equal probability for each birth date.
Frequently asked questions
Why is it called the Birthday Paradox?
It's called a paradox because the results are counterintuitive - most people expect you'd need many more people for a high probability of shared birthdays.
How many people give a 50% chance of shared birthdays?
Just 23 people create a 50.7% probability that two people share the same birthday, which surprises most people.
Does this account for leap years?
Most calculators use 365 days for simplicity. Including leap years would slightly change the probabilities but the overall pattern remains the same.